1. Field of the Invention
The present invention relates to a radiation image capturing system, and in particular, relates to a radiation image capturing system which uses a radiation image capturing apparatus to perform radiation image capturing in a radiography room.
2. Description of the Related Art
Various kinds of the so-called direct-type radiation image capturing apparatus and the so-called indirect-type radiation image capturing apparatus have been developed. The direct-type radiation image capturing apparatus generates electric charges using detection elements according to the radiation dose of, for example, received X-rays and converts the electric charges into electric signals. The indirect-type radiation image capturing apparatus first converts received radiation into electromagnetic waves of another wavelength such as visible light by using, for example, a scintillator, generates electric charges according to the amount of energy of the converted electromagnetic waves using photoelectric conversion elements such as photodiodes and then converts the electric charges into electric signals (i.e. image data). In the present invention, the detection elements of the direct-type radiation image capturing apparatus and the photoelectric conversion elements of the indirect-type radiation image capturing apparatus are collectively called radiation detection elements.
Radiation image capturing apparatuses of these types are known as FPD (Flat Panel Detector), and each used to be formed integrally with a support (or Bucky device) and called by such a name as a specialized-type (for example, refer to Japanese Patent Application Laid-Open Publication No. hei 09-73144). Recently, portable radiation image capturing apparatuses of these types made by placing radiation detection elements and other parts in a housing have been developed and put into practical use (for example, refer to Japanese Patent Application Laid-Open Publication No. 2006-058124 or Japanese Patent Application Laid-Open Publication No. hei 06-342099).
As shown in, for example, FIG. 2 or 3 described below, in these radiation image capturing apparatuses, normally radiation detection elements 7 are arranged two-dimensionally (in a matrix) over a detection unit P, and switch elements constituted of thin film transistors (hereinafter referred to as TFTs) 8 are connected to the radiation detection elements 7 one-to-one.
Usually, radiation image capturing is performed by a radiation generation apparatus 55 (see FIG. 4 described below) irradiating (i.e. emitting radiation to) a radiation image capturing apparatus through a predetermined radiography part of the body of a subject (front chest or lateral lumbar, for example).
At the time, the radiation is emitted in a state in which OFF voltage is applied to lines L1 to Lx of scan lines 5 from a gate driver 15b of a scan driving unit 15 of the radiation image capturing apparatus to set all the TFTs 8 to an OFF state (an electric charge accumulation state described below). Accordingly, the electric charges generated in the radiation detection elements 7 are accumulated therein for sure by the irradiation.
After the electric charge accumulation state, ON voltage is sequentially applied to the lines L1 to Lx of the scan lines 5 from the gate driver 15b to sequentially set the TFTs 8 to an ON state, and the electric charges generated in the radiation detection elements 7 and accumulated therein by the irradiation are sequentially released to signal lines 6 and read out as image data D by readout circuits 17, whereby an image data D readout process is performed.
In order to appropriately perform radiation image capturing, it is necessary that when the radiation image capturing apparatus is irradiated, OFF voltage is appropriately applied to the lines L1 to Lx of the scan lines 5 from the gate driver 15b to set the TFTs 8 as the switch elements to the OFF state.
Hence, for example, a conventional specialized-type radiation image capturing apparatus is often configured to build an interface between the radiation image capturing apparatus and a radiation generation apparatus so as to send/receive signals or the like to/from the radiation generation apparatus, and make the radiation generation apparatus emit radiation to the radiation image capturing apparatus after applying OFF voltage to the lines L1 to Lx of the scan lines 5 and then confirming that the radiation image capturing apparatus is in the electric charge accumulation state.
However, for example, when manufactures of a radiation image capturing apparatus and a radiation generation apparatus are different, it is not always easy to build an interface between the radiation image capturing apparatus and the radiation generation apparatus or it may be impossible to build the interface.
In the case of no interface between a radiation image capturing apparatus and a radiation generation apparatus, the radiation image capturing apparatus cannot know the timing at which the radiation generation apparatus emits radiation thereto. Therefore, the radiation image capturing apparatus itself needs to detect that the radiation is emitted from the radiation generation apparatus, namely, itself needs to detect irradiation thereof by the radiation generation apparatus.
Then, various kinds of such radiation image capturing apparatuses each configured to itself detect start of irradiation thereof have been developed with no interface between the radiation image capturing apparatus and a radiation generation apparatus.
For example, there is described in U.S. Pat. No. 7,211,803 or Japanese Patent Application Laid-Open Publication No. 2009-219538 that when irradiation of a radiation image capturing apparatus starts, electric charges are generated in radiation detection elements 7, the generated electric charges flow out from the radiation detection elements 7 into bias lines 9 (see FIG. 2 or 3 described below) connected thereto, and the amount of current flowing in the bias lines 9 increases. Then, it is proposed therein that the bias lines 9 are provided with a current detection unit to detect the current value of the current flowing in the bias lines 9, and start of irradiation thereof or the like is detected on the basis of the current value.
However, according to the studies of the inventors of the present invention et al., it has been found that the above method has some problems which cannot be solved easily. One of the problems is that because the bias lines 9 are connected to electrodes of the radiation detection elements 7, the noise generated in the current detection unit is transmitted to the radiation detection elements 7 via the bias lines 9, and the noise is superimposed on the image data D read out from the radiation detection elements 7.
The inventors of the present invention et al. carried out various studies to find alternative methods for detecting irradiation with a radiation image capturing apparatus itself, and succeeded in finding several methods which enable accurate detection of start of irradiation with a radiation image capturing apparatus itself (refer to International Publication No. WO 2011/135917 or International Publication No. WO 2011/152093).
By the way, as described in Japanese Patent Application Laid-Open Publication No. 2012-143472, in the case where a radiation image capturing apparatus itself detects start of irradiation thereof, it is necessary that parameters for the processes performed by the radiation image capturing apparatus are appropriately adjusted, and sensitivity to detect start of irradiation thereof is adjusted to a level at which start of irradiation thereof can be accurately detected. It is known that the sensitivity also depends on the irradiation characteristic of a radiation generation apparatus which irradiates the radiation image capturing apparatus.
According to the studies of the inventors of the present invention et al., it has also been found that there is a case where the sensitivity is adjusted as described above, and a radiation image capturing apparatus itself can accurately detect start of irradiation thereof by a radiation generation apparatus when radiation image capturing of the front chest of a certain subject (i.e. a patient or the like) is performed in a certain radiography room, but the radiation image capturing apparatus cannot accurately detect start of irradiation thereof when the subject is moved to another radiography room and radiation image capturing of the front chest of the subject is performed in that radiography room.
Further, even in the same radiography room, when a radiation generation apparatus which irradiates the radiation image capturing apparatus is replaced by another, as with the case described above, the following may occur; a radiation image capturing apparatus can accurately detect start of irradiation thereof when a radiation generation apparatus irradiates the radiation image capturing apparatus, but the radiation image capturing apparatus cannot detect start of irradiation thereof when another radiation generation apparatus irradiates the radiation image capturing apparatus.
Further, for example, when a radiation image capturing apparatus is taken to a patient's room where a patient is hospitalized or a home of a patient, and radiation image capturing is performed therein by a portable radiation generation apparatus irradiating the radiation image capturing apparatus, the following may occur; a radiation image capturing apparatus can detect start of irradiation thereof in a radiography room of a hospital, but the radiation image capturing apparatus cannot detect start of irradiation thereof in a patient's room of a hospital or the like and cannot appropriately perform radiation image capturing.
Thus, according to the studies of the inventors of the present invention et al., it has been found that whether or not a radiation image capturing apparatus can detect start of irradiation thereof depends on radiation generation apparatuses.
When a radiation image capturing apparatus cannot detect start of irradiation thereof although a radiation generation apparatus irradiates the radiation image capturing apparatus through a subject, the radiation image capturing apparatus cannot move to the electric charge accumulation state or the image data D readout process. Consequently, the radiation image capturing apparatus needs, for example, to increase its sensitivity to detect start of irradiation thereof, and then radiation needs to be emitted to the same subject again to capture a radiation image of the subject.
It means that the first time's irradiation is a waste. In addition, the exposed dose to the subject unnecessarily increases, and accordingly burden is unnecessarily imposed on the subject. Further, operability of the radiation image capturing system decreases, such as usability of the radiation image capturing system including the radiation image capturing apparatus and the radiation generation apparatus for operators such as radiologists (hereinafter “operator(s)”) decreases.